Cellulosic hollow fibers, generally known as CUPROPHAN.RTM. hollow fibers, are extensively used in so-called artificial kidneys as a preferential means for removing middle molecule substances, such as uremic toxins, from blood of a patient suffering from a kidney disease. Usually, said hollow fibers are delivered in a dry condition, and prior to use in artificial kidneys they have to undergo treatments to restore their hydraulic permeabilities (filtration of water and diffusive permeabilities) which cause the clearance in dialysis membranes.
According to the prior art such dry cellulosic hollow fibers, as delivered, were first rinsed with either alcoholic solutions or fluorinated hydrocarbons to remove isopropyl ester which was used to maintain the dimension stability of the hollow fibers during transport, storage etc. Thereafter, the rinsed hollow fibers were treated with an alcoholic/glycerol mixture and dried.
It is general state of knowledge that a following treatment, i.e. a treatment after said rinsing, with solutions of high water content and following drying will reduce the membrane permeability (hydraulic permeabilities as defined above), and more generally it was thought that every type of wetting the cellulosic hollow fibers with following drying will reduce the above permeabilities. Additionally, it was stated that radiation sterilization of cellulosic hollow fibers will reduce the hydraulic permeability and the diffusive permeability. A similar reduction of properties is caused on dry CUPROPHAN.RTM. membranes when sterilized by temperature, e.g. by steam sterilization.
Surprisingly, it has been found in accordance with the present invention that a cellulosic hollow fiber, possibly after a previous rinsing treatment as defined above, can be treated with an aqueous solution without any substantial loss of permeability characteristics as was expected according to the general state of knowledge. Furthermore, it was found that cellulosic hollow fibers treated according to the invention can be sterilized by radiation without loss of performances (hydraulic and diffusive permeability).
The invention will be explained in more detail in the following.